The present invention relates to a three-dimensional imaging device using a micromirror array lens.
Several three-dimensional imaging devices have been proposed and developed. One of them uses a “depth from focus” criterion and fast response variable focal length lens. It is described in T. Kaneko et al., 2000, “Quick Response Dynamic Focusing Lens using Multi-Layered Piezoelectric Bimorph Actuator,” Proceeding of SPIE Vol. 4075: 24–31. This imaging system uses a variable focal length lens comprised of two thin glass diaphragms with a transparent working fluid and multi-layered piezoelectric bimorph actuator mounted thereon. To get a three-dimensional image, the criterion of “depth from focus” achieves an all-in-focus image and three-dimensional reconstruction, simultaneously. Since the variable focal length lens has a slow focal length change speed of 150 Hz, the system can have only 5 focal plane shifts when about 30 Hz is considered for the afterimage effect of the human eye. Besides, the lens has a small focal plane variation in the range of −4 mm to 4 mm, which limits the possible range of depth and the depth resolution of the three-dimensional image. A high speed, large variation of numerical aperture and large diameter of variable focal length lens is necessary to get a real-time, large range of depth and high depth resolution three-dimensional image.
A most widely used conventional variable focusing system is the one using two refractive lenses. It has a slow response time and complex driving mechanisms to control the relative position of the refractive lenses. Alternatively, variable focal length lenses have been made. Among them, a most advanced variable focal length lens is a liquid crystal variable focal length lens, which has a complex mechanism to control it. Its focal length is changed by modulating the refractive index. Unfortunately, it has a slow response time typically on the order of hundreds of milliseconds. Even though the fastest response liquid crystal lens has a response time of tens of milliseconds, it has a small focal length variation and a low focusing efficiency.
A new three-dimensional imaging device is needed to overcome the problems of the prior arts that used variable focal length lenses that are slow, have small focal length variation and low focusing efficiency, and/or have a complex control mechanism.